Short range microwave system

ABSTRACT

A short range, low power, microwave system for transmitting single channel data (video, audio, computer pulses, etc.) over distances up to approximately one mile at a frequency range of about 12.2 to 12.7 GHZ. The system includes a microwave transmitter wherein the carrier is amplitude modulated by the desired intelligence and a microwave receiver which includes a reflector feed horn, crystal detector assembly, a bias system for the detector and video amplification; the receiver circuit operates to convert the intelligence from the carrier directly into a usable signal without heterodyning.

United States Patent Hufford 1451 Apr. 25, 1972 [54] SHORT RANGEMICROWAVE SYSTEM [21] Appl. No.: 856,685

[52] US. Cl ..325/373, 325/26, 325/67, 329/205 R [51] Int. Cl ..H03dl/l0, H04b 1/22 [58] Field of Search ..325/1l3, 343, 373, 449, 363,325/67, 26, 445; 329/203, 205 R, 179

[56] References Cited UNITED STATES PATENTS 2,468,655 4/1949 Cole et a1..325/445 X 1,624,185 4/1927 Round ..325/373 2,074,887 3/1937 Beshore..329/205 X OTHER PUBLICATIONS Bronwell & Bean, Theory and Applicationof Microwaves 1947pp.213-2lS,233-234 Welch Laboratory Apparatus-Catalogpage 307 copyright 1954 Primary Exarixiner-Robert L. Richardson Att0rne\'William S. Dorman [57] ABSTRACT A short range, low power, microwavesystem for transmitting single channel data (video, audio, computerpulses, etc.) over distances up to approximately one mile at a frequencyrange of about 12.2 to 12.7 01-12, The system includes a microwavetransmitter wherein the carrier is amplitude modulated by the desiredintelligence and a microwave receiver which includes a reflector feedhorn, crystal detector assembly, a bias system for the detector andvideo amplification; the receiver circuit operates to convert theintelligence from the carrier directly into a usable signal withoutheterodyning.

4 Claims, 4 Drawing Figures PATENTEDAPRZS 1972 3,659,204 SHEET 1 OF 2.WAYA/E 7. HUFFORD //VVEN7'0R PATENTEDAPR 25 m2 WWWWWW\\ WAYNE THurranaATTORNEY SHORT RANGE MICROWAVE SYSTEM The present invention relates to ashort range microwave system for transmitting and receiving singlechannel data over distances up to one mile at frequencies in the rangeof 12.2 to 12.7 GI-IZ. More particularly, the present invention relatesto the receiver portion of this microwave system wherein theintelligence is detected from the carrier by means of a novel circuitincluding a crystal detector without any heterodyning and wherein thecrystal detector itself is of novel design.

In most microwave systems operating at or near the frequencies involvedherein, it is generally necessary to employ a klystron or otherexpensive beat frequency equipment to extract the intelligence from theincoming signal using the well known heterodyne principle. Not only isthe particular frequency oscillator expensive in and of itself, but thepower supply circuit therefor is also generally quite expensive. On theother hand, the receiver of the present invention utilizes a crystaldetector, a biassing network and a high-gain solid state amplifier(without any beat frequency oscillator) so as to result in a. low costwith high reliability. A camera can be connected to the transmitter anda monitor can be connected to the output of the receiver; no additionalequipment is required.

It is understood, of course, that cables or other conduits have alsobeen used to transmit intelligence over relatively short distances;however, where the intelligence represents a wide spectrum of differentfrequencies, the attenuation is generally non-uniform for the differentfrequencies such that compensation therefor is required at the remoteend of the cable or conduit. Also, where it is desired to transmitacross busy streets, .over rough terrain or through hazardous areas, thepresent system is feasible where the cable or conduit is not.

Therefore, it is a principal object of the present invention to providea short range microwave system capable of transmitting and receivingsingle channel data over relatively short distances with relativelysimple and inexpensive equipment.

It is a further object of the present invention to provide a short rangemicrowave system which is capable of transmitting information overrelatively short distances where it is not feasible or possible totransmit this information by cable or other conduit.

It is a further object of the present invention to provide a short rangemicrowave system wherein the receiver is adapted to convert theintelligence from the carrier into a usable signal without using theheterodyne principle or the necessary equipment which is generallyrequired when utilizing this principle.

It is still a further object of the present invention to provide amicrowave receiver of the type referred to above which includes a novelcrystal detector, biassing network and high-gain amplifier. 7

Other and further objects and advantageous features of the presentinvention will hereinafter more fully appear in connection with adetailed description of the drawings in which:

FIG. 1 is a semi-diagrammatic representation ofa portion of the receivershowing the antenna, detector and pre-amplifier sections; v

FIG. 2 is a circuit diagram of the video amplifier section of thereceiver which connects with the output from FIG. 1;

FIG. 3 is a side elevation of the crystal detector diagrammaticallyshown in FIG. 1; and

FIG. 4 is a longitudinal sectional view of the crystal detector of FIG.3 showing the internal details thereof.

Referring to the drawings in detail, FIG. 1 shows a parabolic reflectormounted on a wave guide 22 so as to comprise an antenna feed horn. Theleft hand end of the wave guide 22 is properly positioned with respectto the focal point of the reflector 22 so as to maximize signalreception. It should be understood that the above described antenna feedhorn is properly directed towards a signal antenna feed horn (not shown)located at the transmitter (not shown). The transmitter feed horn inturn will be properly directed towards the receiver antenna feed horn.The transmitter will be provided with a modulator-power supply (notshown) including a klystron (not shown), or similar device. Thetransmitter will be capable of producing an output carrier wave of thefrequency referred to herein which carrier is preferably amplitudemodulated by the intelligence which the operator desired to send fromthe point of transmission to the point of reception. The details of thetransmitter are not shown herein since any suitable means for providingan amplitude modulated carrier of the frequency range desired would besuitable for the purposes of the present invention.

In turning to the description of FIG. 1, the wave guide section 22 issuitably aligned with and properly electrically mated with the internalwave guide section 24 at one end of which is mounted the detectorassembly 26 which will be described hereinafter in greater detail. Thelower end of the detector assembly 26 is connected to a fixed biasresistor R, which, in turn, connects with variable bias resistor R theother end of the bias resistor R connects with a fixed bias voltage ofapproximately 1.5 volts, the negative terminal of this voltage sourcebeing connected to ground as shown.

The signal developed at the upper end of the bias resistor R, is fedinto terminal No. 3 of an integrated circuit, which, in this instance,is CA3018, the internal details of which are well known and, hence, notdescribed. The input terminal No. 3 is also connected to ground througha filter circuit consisting of R and C Terminal No. 4 is grounded asshown and terminal No. 2 connects with terminal No. 3 through resistor Rto ground through resistor R Terminal No. l connects to ground throughresistor R and capacitor C connected in parallel. A bias voltage of sixvolts is applied directly to terminal No. 8 and through resistor R toterminals No. 5 and 9 in common. An intermediate bias voltage is appliedto terminal No. 12 at the junction of resistors R and R which connect inseries between the six volt source and terminal No. 9.

For the purposes of this description, terminal No. 7 will be consideredas the output terminal of the integrated circuit and the output signalis developed across resistor R The output signal is fed throughcapacitor C and the potentiometer R The output from FIG. 1 appears onlead 28 which connects with the center arm of the potentiometer RTurning now to FIG. 2, lead 28 connects through capacitor C to the baseof transistor 0,. In FIG. 2 transistor Q together with transistors 0 andQ constitute a video amplifier. The negative side of a twelve volt d.c.source is applied directly to the collector of 0;. This same negativevoltage is applied to the bases of transistors Q Q and Q throughresistors R R and R respectively. The collector of Q, connects with thenegative side of the twelve volt source through resistor R The positiveside of the twelve volt source connects with the base of transistor Qthrough resistor R to the emitter of Q through resistor R to the base ofQ through resistor R to the emitter of 0 through resistor R and to theemitter of Q through resistor R The signal coming through the lead 28 isdeveloped across resistor R before being fed into the transistor Qthrough the capacitor C The collector of Q connects to the base of Qthrough capacitor C The outputfrom the emitter of Q, is taken offthrough capacitor C at 30 and should represent a 1.4 AC. signalcorresponding in frequency to the input intelligence received. Feed backfrom the emitter of O to the emitter of Q, is provided through thecapacitor C Referring to FIGS. 3 and 4, the detector assembly 26,briefly described in FIG. 1, will now be set forth in detail. The upperend of the detector assembly is comprised of an RF plug 32 which, byway-of example, could be a standard UG-58A/A U plug. The plug 32 has aflange 34 as shown, is provided with a lower threaded portion 36, isfurther provided with a central pin 38 which is supported internallywithin the plug 32 by means of the Teflon body 40. The lower, inner endof the pin 38 is provided with a small, circular hole 42 for a purposewhich will be hereinafter described. The outer concave portion of theTeflon member 40 is covered with a radial, or circular, resistor whichis made by grinding up carbon, mixing the carbon with glue and applyingit as a layer 44 as shown.

The radial or circular resistor 44 results uponthe drying of the glue.The resulting resistor 44 is symmetrical with respect to any wavereceived in the wave guide assembly previously described.

A crystal assembly 46, which preferably is a 1N78 is attached to thelower inner end of the RF plug in the following manner. The crystalassembly 46 is provided with a Teflon coating or cylinder 48. A thin RFsleeve 50, made of suitable metal such as aluminum or brass is insertedinto the lower end of the plug 32 in a snug fitting relationship.Thereafter, the crystal assembly 46, with the Teflon insulation thereonis inserted inside the RF sleeve 50 until the small internal pin 52(which is part of the crystal assembly 46) is received within the smallhole 42. The crystal assembly 46 is a standard purchased item and,therefore, will not be described in detail except to note that a crystalis mounted within the interior in a suitable encapsulating material, iselectrically connected to the pin 52 and is grounded to the case 46.

After the crystal assembly and RF sleeve have been inserted in the plug32 in the manner described above, a cylindrical RF shield 54 is screwedonto the lower end of the plug 32. The lower end of the RF shield 54 isprovided with a threaded opening 56 which is adapted to receive theupper threaded end of a plug 58'. The latter plug, for example, can be astandard UGlO94/U plug or equivalent. A springcontactor 60 having anupper pointed end is secured at its lower end in a suitable openingprovided in the upper end of the plug 58. The connector 60 is provided acomplete turn 62 to provide the desired resiliency. When the plug 58 isscrewed into the opening 56 the upper pointed end of the contactor60engages the lower surface of the crystal assembly 46; upon screwingthe plug 58 all the way into the hole 56, the resiliency of the springcontactor 60 will insure that the crystal assembly is held securely inthe position shown in H6. 4. For the purpose of permitting electricalcontact with the lower end of the detector assembly, the plug 58 isprovided with a lower hollow contactor 64 to accommodate a pin, forexample, which will connect with R,.

The lower end of the contactor. 60 connects with hollow connector 64 bymeans of wire 66, and these last three-mentioned elements are surroundedby a layer of Teflon 68 to electrically insulate them from the plug 58'.

OPERATION The incoming signal is received by the parabolic reflectorfrom any suitable transmitter (not shown) operating in the preferredrange of [2.2 to 12.7 GHZ. The wave guide sections 22 and 24 arestandard A-inch by l-inch wave guides and, therefore, the transmittercould operate anywhere in the frequency range from 9 GHZ up to 13 GHZand beyond. However, it should be understood that this invention is notlimited to any particular frequency or frequency range. By selecting adifferent size of wave guide and a different transmitter, the inventionis capable of operation over a wide range of frequencies. The details ofthe transmitter have not been shown, but it should be understood thatany suitable transmitter which is capable of operating in the frequencyranges referred to above with amplitude modulation would be acceptablefor the purposes of the invention.

The signal received by the parabolic reflector 20 is introduced to thewave guide section 22 at the approximate focal point of the antenna asis well known to those skilled in this art. The signal is transmittedfrom the wave guide section 22 to the wave guide section 24 also usingthose principles which are well known in this art. A suitable choke isprovided on either wave guide 22 or 24 to permit proper conduction fromone wave guide section into the other. Within the wave guide section 24,the pin 38 is properly positioned with respect to the end of the waveguide to, maximize the signal received.

The radial resistor 44 will produce the proper impedance,

match required and also presents a symmetrical termination for the biasnetwork later to be described. It should be noted that the point where.the radial resistor 44 contacts the flange 34 is at ground potential.

The signal received by the pin 38 represents the carrier plus theintelligence. The intelligence is detected from the carrier by thecrystal which is shown in the interior of the crystal case 46. Thecrystal will also detect the carrier itself but this is bled off orshorted out through the capacitor which is created by the physical spacebetween the outside cylindrical portion of the case 46 and the RF sleeve50, the dielectric in this case being the Teflon coating 48. Obviously,any other suitable dielectric might be employed. The detectedintelligence is developed across the top of resistor R,; a bias systemis created from the 1.5 volt source through resistors R R,, the

crystal itself and radial resistor 44. The bias across the crystal canbe varied by adjusting the resistance of R When making this adjustment,R is adjusted for maximum output at point 28, point 30, or the terminalNo. 3 on the integrated circuit.

As indicated previously, the signal developed across the top of R isintroduced to the integrated circuit at terminal No. 3. Furtherdescription of the internal details of the integrated circuit and thetransistors Q Q and Q, is believed to be unnecessary except insofar asto state that thisv circuitry has been designed to amplify whateverintelligence is imposed upon the carrier received whether thisintelligence is video, audio or computer pulses. Accordingly, the outputfrom point 30 is fed to a suitable monitor which is capable ofreproducing the type of signal superimposed on the carrier by the audio,video (black and white or color) or computer information.

Whereas the present invention has been described in particular relationto the drawings attached hereto, it should be understood that other andfurther modifications, apart from those shown or suggested herein, maybe made within the spirit and scope of this invention.

What is claimed is:

1. A short range, low power, microwave system for transmitting andreceiving. single channel data which includes a microwave receivercapable of receiving an amplitude-modulated microwave .carrier, saidmicrowave receiver including a receiving antenna, a crystal detectorconnected directly to the receiving antenna, a first symmetricalresistor connected from said antenna to ground, a second resistorconnected to said crystal detector, a bias means connected in serieswith said crystal detector and said resistors for biasing said crystal,high frequency capacitance means surrounding said crystal and means foramplifying the signal produced at the point of connection between saidcrystal detector and said second resistor.

2. A microwave system as set forth in claim 1 including an RF shieldsurrounding said high frequency capacitor and crystal detector.

3. A microwave system as set forth in claim 1 wherein said antennacomprises a pin which projects upwardly into and is properly positionedwithin a wave guide which receives the microwave signal. 1 t

4. A crystal detector for a microwave receiver comprising asubstantially cylindrical crystal assembly containing a crystal therein,a support means for said crystal assembly, a centrally disposed andupwardly projecting pin located within said support means andelectrically insulated therefrom, said pin being adapted to projectupwardly into a wave guide at a position for the optimum reception of amicrowave signal, the other end of said pin being electrically connectedto said crystal, a radial resistor positioned on said support meanssymmetrically disposed about said pin, said symmetrical resistor beingconnected at one end to said pin and at the other end to said supportmeans, a radio frequency sleeve positioned within said support meansbetween said support means and said crystal assembly, a non-conductivesleeve positioned between said radio frequency sleeve and said crystalassembly, said crystal assembly, non-conductive sleeve and radiofrequency sleeve constituting a microwave condenser, a radio frequencyshield connected to said support and surrounding said crystal as semblyand said sleeves, a spring contactor mounted within said radio frequencyshield and insulated therefrom, one end of said spring contactorengaging said crystal assembly and urging the same into contact withsaid pin, the other end of said spring contactor being electricallyconnected to an electrical connection external of said radio frequencyshield.

1. A short range, low power, microwave system for transmitting andreceiving single channel data which includes a microwave receivercapable of receiving an amplitude-modulated microwave carrier, saidmicrowave receiver including a receiving antenna, a crystal detectorconnected directly to the receiving antenna, a first symmetricalresistor connected from said antenna to ground, a second resistorconnected to said crystal detector, a bias means connected in serieswith said crystal detector and said resistors for biasing said crystal,high frequency capacitance means surrounding said crystal and means foramplifying the signal produced at the point of connection between saidcrystal detector and said second resistor.
 2. A microwave system as setforth in claim 1 including an RF shield surrounding said high frequencycapacitor and crystal detector.
 3. A microwave system as set forth inclaim 1 wherein said antenna comprises a pin which projects upwardlyinto and is properly positioned within a wave guide which receives themicrowave signal.
 4. A crystal detector for a microwave receivercomprising a substantially cylindrical crystal assembly containing acrystal therein, a support means for said crystal assembly, a centrallydisposed and upwardly projecting pin located within said support meansand electrically insulated therefrom, said pin being adapted to projectupwardly into a wave guide at a position for the optimum reception of amicrowave signal, the other end of said pin being electrically connectedto said crystal, a radial resistor positioned on said support meanssymmetrically disposed about said pin, said symmetrical resistor beingconnected at one end to said pin and at the other end to said supportmeans, a radio frequency sleeve positioned within said support meansbetween said support means and said crystal assembly, a non-conductivesleeve positioned between said radio frequency sleeve and said crystalassembly, said crystal assembly, non-conductive sleeve and radiofrequency sleeve constituting a microwave condenser, a radio frequencyshield connected to said support and surrounding said crystal assemblyand said sleeves, a spring contactor mounted within said radio frequencyshield and insulated therefrom, one end of said spring contactorengaging said crystal assembly and urging the same into contact withsaid pin, the other end of said spring contactor being electricallyconnected to an electrical connection external of said radio frequencyshield.